1. Field of the Invention
The present invention relates to a DNA sequence, a polypeptide encoded by this sequence, and to the use of said DNA sequence and polypeptide in the production of amorphadiene.
2. Description of the Related Art
Human malaria is a commonly occurring widespread infectious disease, caused in 85% of the cases by Plasmodium falciparum. This parasite is responsible for the most lethal form of malaria, malaria tropicana. Each year, malaria causes clinical illness, often very severe, in over 100 million people of which eventually over 1 million individuals will die. Approximately 40% of the world's population is at risk of malaria infection (as estimated by the World Health Organization).
Malaria has traditionally been treated with quinolines, such as quinine, chloroquine, mefloquine and primaquine, and with antifolates. Unfortunately, most P. falciparum strains have become resistant to chloroquine, and some have developed resistance to mefloquine and halofantrine as well. Thus, novel antimalarial drugs to which resistant parasites are sensitive are urgently needed. Artemisinin, as well as its semisynthetic derivatives are promising candidates here.
Artemisinin (FIG. 1), [3R-(3α, 5aβ, 6β, 8aβ, 9α, 12β, 12aR*)]-Octahydro-3,6,9-trimethyl-3,12-epoxy-12H-pyrano[4,3-j]-1,2-benzodioxepin-10(3H)-one; molecular weight 282.35), also called arteannuin, qinghaosu or QHS, is a sesquiterpene lactone endoperoxide isolated from the aerial parts of the plant Artemisia annua L.
Artemisia annua L., also known as quinghao (Chinese), annual or sweet wormwood, or sweet annie is an annual herb native to Asia. A. annua, a member of the Asteraceae, belongs to the tribe Anthemideae of the Asteroideae, and is a large herb often reaching more than 2.0 m in height. It is usually single-stemmed with alternating branches. The aromatic leaves are deeply dissected and range from 2.5 to 5 cm in length. Artemisinin is mainly produced in the leaves as a secondary metabolite at a concentration of 0.01–0.6% on a dry weight base in natural populations. Artemisinin is unique to the plant A. annua with one possible exception of A. apiacea L. The A. annua used in this invention is of Vietnamese origin.
Because of its low concentration in plants, artemisinin is a relatively expensive resource for a drug. Current research has thus been aimed at producing artemisinin at a larger scale by organic synthesis. However, because artemisinin consist of seven chiral carbon atoms, theoretically 27=128 isomers can be formed of which only one is identical to artemisinin. Because of this complex structure of artemisinin, production of this compound by organic synthesis is not profitable from a commercial point of view.
Genetic engineering of the biosynthetic pathway of artemisinin may give rise to higher artemisinin levels in plants. To be able to interfere in the biosynthesis of artemisinin, the biosynthetic pathway has to be known, either completely or partially. Several attempts to elucidate the entire biosynthetic pathway have been undertaken. Until now, however, the exact pathway has remained largely unknown.